1. Field of the Invention
This invention is related to cavitation inducing nozzles for rock bits operating in hydraulic drilling mud.
More particularly, this invention provides a means to convert a rock bit with one or more conventional nozzles to cavitation-inducing nozzles by securing a cavitation-inducing device adjacent the exit end of the nozzles. The converted nozzles enhance the penetration rate of the rock bit.
2. Description of the Prior Art
The use of the cavitation phenomenon to erode solid material is taught in U.S. Pat. Nos. 3,528,704 and 3,713,699.
The earlier '704 patent describes a method for utilizing the normally destructive forces of cavitation to provide an erosion effect for accomplishing drilling, boring and like functions of solids which comprise forming a fluid jet by directing the fluid through a restricted orifice at speeds sufficient to generate vapor-filled bubbles in the jet and impinging the jet against the solid at a distance from the orifice where the vapor bubbles collapse or implode, catastrophically penetrating the solid material.
The patent describes and illustrates fluid under pressure that is forced out of an exit opening which necks down from an upstream chamber. In most embodiments, a central concentric rod or pintle is introduced near the exit opening to induce cavitation as the liquid is forced out of the exit orifice. The resultant formation, growth and collapse of vapor-filled cavities or "bubbles" in a flowing liquid that occurs at a level where local pressure is reduced below the vapor pressure of the liquid causes the erosion of the solid material. The implosion of the collapsing cavity happens with such violence it damages and erodes the material with which it comes into contact.
The later '699 prior art patent teaches a slight improvement in the destructive power of the cavitation phenomenon by surrounding the cavitating jet with a liquid medium.
The following U.S. Pat. Nos. 4,185,706 and 4,187,921, assigned to the same assignee as the present invention, teach the use of cavitation nozzles in combination with rock bits.
The cavitation nozzles taught in the '706 patent enhance the drilling rate by creating catastrophic implosion waves which erode solid material at the bottom of the hole while reducing the localized pressure at the rock tooth interface. Localized pressure reduction reduces the tendency for the cuttings to adhere to the bottom of the hole due to differential pressure.
The '921 patent teaches the use of one or more cavitation-inducing nozzles in combination with conventional nozzles for rock bits. The cavitation nozzles enhance the drilling rate by rapidly removing cuttings from the hole bottom. Cavitation from a cavitating nozzle positioned on one side of the bit reduces the pressure, thereby inducing drilling mud at higher pressure passing through an opposing non-cavitative nozzle to move across the rock tooth interface. The resultant crossflow rapidly removes the cuttings from the hole bottom.
The present invention advances the state of the art in that a separate flow cavitation device may easily be attached adjacent a conventional nozzle already installed within a rock bit without major modification or disassembly/assembly problems.